1. Field of the Invention
The present invention relates to an image forming apparatus that includes a container in which waste toner is collected.
2. Description of the Related Art
As is well known, when an electrostatic latent image is formed on a photosensitive element serving as an image carrier in an image forming apparatus, the latent image is developed into a toner image by toner supplied from a developing device, and the toner image is transferred and fixed onto a recording sheet.
In addition to a single-color image, an image with a plurality of colors including a full-color image is formed in the image forming apparatus. In this case, it is necessary that images having different colors are superimposed and transferred.
In some cases, the image forming apparatus includes a waste toner tank in which residual toner (waste toner) left after cleaning a photosensitive element or a transfer element is collected.
It is necessary to replace the waste toner tank when the waste toner tank is full of collected waste toner. Therefore, it is important to accurately determine replacement time to replace the waste toner tank to prevent overflow of waste toner.
Currently, various image forming apparatuses have been disclosed that include a configuration for detecting the replacement time of the waste toner tank, i.e., determining whether the waste toner tank is full of waste toner, and automatically stopping operation at the replacement time. For example, Japanese Examined Utility-Model Application publication No. H05-015603 and Japanese Patent Application Laid-open No. H05-313434 disclose a configuration in which a waste toner tank is formed of a transparent body, and it is determined whether the waste toner tank is full of waste toner based on a change of intensity of light transmitted through the waste toner tank. Moreover, Japanese Patent Application Laid-open No. H05-188835 discloses a configuration in which an amount of waste toner filled in the waste toner tank is divided into a first full level and a second full level, and two detecting sensors are provided to detect the full levels, respectively. When the first full level is detected, a first waste toner full is notified to alarm that the waste toner tank will soon be full of waste toner. When the second full level is detected, a second waste toner full is warned, which indicates that the waste toner tank is full of waste toner, and the operation is automatically stopped.
However, in the configuration disclosed in Japanese Examined Utility-Model Application publication No. H05-015603 and Japanese Patent Application Laid-open No. H05-313434, when the waste toner tank is full of waste toner, the operation makes a sudden stop. Therefore, if a user does not have a spare waste toner tank, it may take a long time to recover the operation.
In the configuration disclosed in Japanese Patent Application Laid-open No. H05-188835, it is necessary to arrange two detecting units because two-level detecting system is employed. Thus, a space to arrange the detecting units may be needed or the whole image forming apparatus may be complicated in configuration. Particularly, when the number of detecting units is increased, it may take efforts in maintenance checks or replacement of a waste toner tank, thereby causing another problem in addition to replacement of the waste toner tank.
Typically, a service engineer from a manufacturer of the apparatus often replaces a waste toner tank. Even if a user gets in contact with the service engineer when a waste toner tank is full or nearly full of waste toner, the service engineer cannot immediately respond to the request from the user. Therefore, the service engineer checks an amount of waste toner remaining in the waste toner tank by sight in regular visits and roughly determines an amount of waste toner that can be filled in the waste toner tank. When the service engineer determines that the waste toner tank will be full of waste toner by the next visit, the service engineer generally replaces the waste toner tank. Thus, it is possible to reduce interrupt time during image forming processing, that is, apparatus downtime for a user. However, when a workload difference among users is considered, the waste toner tank may be replaced even if it has much room for accommodating waste toner. This may result in useless expense for replacing the waste toner tank.